Each subject was shown a printed word on a computer screen that was either

UNMASKED and hence VISIBLE or MASKED and hence INVISIBLE.

Here's the set-up.

First (in every presentation, both masked and unmasked)

a row of hatch marks (#########) was shown on the screen as a meaningless mask.

Next, a printed word likecousin was flashed on the screen very briefly

(for only 29 milliseconds (msec)) – a thirtieth of a second.

Next, to make the word invisible during the MASKED presentation,

a row of ampersands would be flashed &&&&&&&&&& for 400 msec.

The effect of this MASK was to retroactively interfere with the neural processing of the word.

With masking, the subjects could not guess the words or even the gist of the words

(whether they were threatening words like "kill" or "danger" or non-threatening words like "cousin" or "see.") (However, note, that the printed word would still have appeared

on the subject's retinas and caused something to happen in their visual systems,

even though they could report nothing.)

The other half of the time, rather than being masked by the &&&&&&&&&&,

the printed word would again be presented for 29 msec,

but then would simply be followed by a blank screen (no mask).

Since there was nothing to interfere or mask the visual experience of the printed word,

the subjects were able to say the printed word that they saw - they had actually "seen" it.

So, the million dollar question was this...

what was going on in the brains of the patients when they actually SAW

the unmasked or visible printed word (in comparison to the same word when it was masked).

The above figure compares unconscious responses on the left to conscious responses on the right. In the conscious column (right-hand) note the intense, high-frequency responses that begin around 200 msec and last for another 400 msec or so. That is the signature of global resonance.

Here's the bottom line, and I've simplified it for this summary.

Both the masked words and the unmasked words excited the early stages of visual processing

in the occipital lobe (back of the brain). After all, even the masked words were detected,
ie, processed by the retina. However, just that early, brief processing in the occipital lobe was

not sufficient to give rise to the subjective experience of seeing and identifying the word.

For consciousness to occur, what had to happen was this.

The initial wave of visual processing of the printed word in occipital (and then temporal lobe)

had to be sufficiently long and intense to excite neurons in the prefrontal cortex (front of the head).

Once prefrontal cortex was excited, it would then cause a wave of feedback to the occipital and temporal lobes that would amplify their excitation. This would result in a long-lasting reverberation between the the front of the brain and the back of the brain.

This, then, appears to be the defining characteristic of consciousness:

Condition 1: information must be explicitly represented by the neuronal ﬁring of perceptual

networks located in visual cortical areas coding for the speciﬁc features of the conscious percept.

Condition 2: this neuronal representation must reach a minimal threshold of duration and intensity

necessary for access to a second stage of processing, associated with a distributed corticalnetwork involved in particular parietal and prefrontal cortices.

Condition 3: through joint bottom-up propagation and top-down attentional ampliﬁcation, the ensuing brain-scale neural assembly must ‘‘ignite’’ into a self-sustained reverberant state of coherent activity that involves many neurons distributed throughout the brain."

The data that they uncovered precisely supports this theory. The key difference that they showed between the neural response to the masked words and the unmasked or visible (consciously seen) words was this:

"Nonconscious processing of words elicited short-lasting activity across multiple cortical areas, including parietal and visual areas. In sharp contrast, only consciously perceived words were accompanied by long-lasting effects (200 ms) across a great

variety of cortical sites, with a special involvement of the prefrontal lobes.

This sustained pattern of neural activity was characterized by a specific increase of coherence between distant areas, suggesting conscious perception is broadcasted widely across the cortex."

In particular, when their human subjects actually saw the words (unmasked) their neural responses showed sustained voltage changes especially in the prefrontal cortex

(the executive area of the brain) and large increases in gamma power. (Gamma is the highest frequency band on the eeg (above 30 hz ) and is a well-known hallmark of conscious awareness.) Their last two findings - long-distance phase synchrony and long-distance Granger causality - are also important, since they show that all the areas connected are actually communicating information. They are not only in-phase but causally connected. Here are some relevant quotes.

"These observations ﬁt with the global workspace model, which postulates that once a representation is consciously accessed, a broad distributed network, involving in particular prefrontal cortex, ignites and broadcasts its content. Computer simulations of this ignition process within thalamo-cortical networks have shown strong recurrent interactions

occuring exclusively during conscious access, implying that the relevant neurons are suddenly coactivated in a cooperative manner and emit increased and synchronized high-frequency oscillations in the gamma range."

long-distance exchange of information across a very broad cortical network. Long-distance coherence between distant regions appears to co-occur with the active maintenance of locally coded representations. ...

These observations are consistent with global workspace theory’s prediction that conscious access occurs during a late time period and is dominated by an in-ﬂow of perceptual information from posterior visual areas into higher frontal and parietal cortices."

A simplified explanation is that the areas where the detailed encoding of visual information occurs in the back of the brain are excited in a sustained manner by the areas which they excite in the front of the brain (prefrontal cortex). The widespread reverberation that ensues is an essential neural correlate of consciousness (NCC).

These findings are moving us toward a solution to the “easy problem” of consciousness – what are its neural correlates. The hard problem remains – how does a diffuse, oscillating